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Weatherizing Your Attic - Locating and Correcting Air Leaks

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How to locate and insulate gaps around wiring, piping, and framing inside your attic.

The average single family home has the equivalent of an open window leaking heated air into your attic or around your windows and doors. Most gaps and holes are the size of a dime, but when you combine all of these gaps around plumbing pipes, electrical fixtures, chimneys and other attic spaces it adds up to a poorly weatherized home.

All it takes to remedy this problem are a few inexpensive materials half of your weekend to save money on your home heating costs every year by sealing these holes. This article will illustrate some of the most common problem areas and how to fix them.

Along with the obvious effect of saving money on your home heating costs, by sealing the sources of air leakage into the attic you will reduce the chances of ice dam formation and potential water damage.

Infrared image of attic air leakage


It is a good idea to make a sketch of your home before you go into the attic. You should layout the locations of bathrooms, chimneys, and electrical fixtures to use as a reference when you are up in the attic.

To help find hidden leaks you should install a box fan in an open window so that it blows air into the home. Make sure all other windows and openings are closed. Seal around the fan with foam insulating board or cardboard cut to cover the gaps between the fan and window jamb.

Tools and Materials

Caulk gun

Dust mask


Knee pads

Safety glasses

Utility knife

Unfaced fiberglass insulation

Garbage bags

Foam insulating board

Acrylic latex caulk

High temperature silicone caulk

Expanding spray foam insulation – fire rated foam is recommended

Foam weatherstripping

Foam Weatherstripping


While larger areas are usually well insulated, the spaces above showers and soffits can have fallen and missing insulations that allow huge amounts of air to flow through them. Blown in insulation is often a source of this type of attic air leakage.

Place the unfaced insulation inside plastic garbage bags to act as a vapor barrier and stuff the fiberglass insulation down into the stud cavities.

Be careful to keep the insulation away from recessed light fixtures unless they are marked “IC” for insulation contact. IC rated light fixtures can come in contact with insulation without the risk of fire.

For showers and above soffits, place rigid foam board insulation across the bay and caulk the edges to seal. Place unfaced insulation on top of the foam.

Piping and Ductwork Chases

A chase is a continuous opening between floors to allow piping, electrical wiring, or HVAC ductwork to pass through. While most homes may not have a piping chase, 2-story homes may have an opening from the basement to the attic near stairwells that have not be properly sealed.

An open HVAC chase from the basement to the attic

Another type of chase is where the stud cavity is used as a return air duct. Occasionally the top plate may have been cut away or removed during construction. Cut a piece of ¾-inch plywood or a scrap 2x4 to cover the hole. Replace the attic insulation above the chase.

Plumbing Vents and Electrical Fixtures

Large gaps are usually found around plumbing vents. Most builders will not take the time to cut a round hole for a pipe, but instead cut out a section of the top plate to allow the plumbing vent, usually a 3 or 4-inch PVC pipe to pass through. For very large holes you can stuff small pieces of fiberglass insulation into the space around the plumbing vent pipe and cover it with expanding foam. Follow the directions on the can to fill the space around the pipe with expanding foam insulation. Wear safety glasses and rubber gloves to keep the material off of your hands.

Foam around plumbing vents

Foam around piping

Fill wiring with caulking or expanding foam. Caulk around electrical junction boxes and fill holes in the box with caulk. Ceiling fan boxes can enlarge holes if the fans are not balanced properly. Caution: Never use expanding foam when insulating electrical boxes, the foam can enter the box and cause the wiring to overheat.

Caulk holes on electrical boxes and between the box and the drywall

Lifting insulation batts will show evidence air leakage. Inspect the insulation carefully and look for areas where the insulation is darkened by dirt. During winter months you may observe frost on the surface of the insulation caused by warm, moist air condensing and freezing as it hits the cold attic air. In warmer weather, you may find water staining in these same areas. Pressurizing the house with a window fan will help you locate leaks with your hand as the air finds its way into the attic.

Look for dirt around electrical boxes and on the insulation

Attic Door

Weatherstripping the attic access hatch or door is an excellent way to reduce air leakage. Cut 1x2 pine boards to fit the perimeter of the attic opening and nail them into the existing attic opening with 6d finish nails. Apply self-adhesive foam weatherstripping tape to the top edge of the stop. This will reduce air leakage around the hatch. To increase the effectiveness of the sealing, install hook and eyes on opposite sides of the access panel to pull the plywood down onto the weatherstripping.

Weatherstripping an attic access panel

Make sure that there is at least a 12 inch high border around the attic access panel to prevent the insulation from falling onto the panel or disturbing it when you go up into your attic. The border can be made out of ¾-inch plywood or rigid foam insulation boards.

Tips and Tricks

  • Try to work in the early morning, or when the outside temperature is below 75 degrees.
  • Wear long sleeves to protect your arms from irritating fiberglass insulation.
  • Always wear an OSHA-approved particulate respirator.
  • Use scraps of plywood to kneel on and to prevent compressing the insulation.
  • Never step on the ceiling drywall.
  • Don’t force insulation into attic eaves or soffit vents.
  • Carry a flashlight as a backup in case your work light breaks or the attic light burns out. Also, use rough service shatter-resistant bulbs which have a Teflon coating to prevent broken glass from covering the attic insulation. (One brand name for shatterproof incandescent light bulbs is Shat-R-Shield.)



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Posted on Oct 11, 2011
Posted on Oct 10, 2011
Roberta Baxter
Posted on Oct 10, 2011

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Daniel Snyder

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